Aire-flo furnace blinks three times after trying to start. Inducer motor/fan turns fine, ignitor has continuity but doesn't glow, pressure switch is good.

Are you sure the control board is good? I would look at that before going elsewhere.

TRI-COLOR (DSI LED) DIAGNOSTIC TABLE
No. of Red BLINKS
1 Flame sensed when no flame should be present
Verify the gas valve is operating and shutting down properly. Flame in burner assemble should extinguish promptly at the end of the cycle. Check orifices and gas pressure.

2 BLINKS Pressure switch stuck closed/ inducer error
Pressure switch stuck closed. Check switch function, verify inducer is turning off.

3 BLINKS 1st-stage pressure switch stuck open/inducer error
Check pressure switch function and tubing. Verify inducer is turning on the pulling sufficient vacuum to engage switch.

4 BLINKS Open limit switch Verify continuity through rollout switch circuit.

5 BLINKS Open rollout/open fuse detect Verify continuity through rollout switch circuit, check fuse.

6 BLINKS 1st-stage pressure switch cycle lockout If the first stage pressure switch cycles 5 times (open, closed) during one call for heat from the thermostat the control will lockout.Check pressure switch for fluttering, inconsistent closure or poor vacuum pressure.
7 BLINKS External lockout (retries exceeded) Failure to sense flame is often caused by carbon deposits on the
flame sensor, a disconnected or shorted flame sensor lead or a
poorly grounded furnace. Carbon deposits can be cleaned with
emery cloth. Verify sensor is not contacting the burner and is locatedin a good position to sense flame. Check sensor lead for shortingand verify furnace is grounded properly.

8 BLINKS External lockout (ignition recycles
exceeded where flame is established and then lost)Check items for exceeded retries listed above and verify valve is not dropping out allowing flame to be established and then lost.

9 BLINKS Grounding or Reversed polarity Verify the control and furnace are properly grounded. Check and reverse polarity (primary) if incorrect.

10 BLINKS Module gas valve contacts energized
with no call for heat Verify valve is not receiving voltage from a short. If a valve wiring is correct and condition persists, replace module.
11 BLINKS Limit switch open - possible blower
failure overheating limit Possible blower failure, restricted air flow through appliance or duct work. Verify continuity through limit switch circuit and correct overheating cause.

12 BLINKS Module Ignitor contact failure Fault code indicates the module ignitor contacts are not functioning
properly. Replace module.Solid Module - internal fault condition Module contacts for gas valve not operating or processor fault.
Reset control. if condition persists replace module.
3 double 2nd-stage Pressure Switch Stuck Open/Inducer Error
Check pressure switch function and tubing. Verify inducer.

When a furnace has a bad ignitor what I see most of the time is the following sequence of operation:

1. On a call for heat
2.The draft inducer motor starts.

3.The pressure switch which has a small plastic or rubber tube attached yo it senses the negative pressure produced by the draft inducer and closes.

4.The draft inducer runs for 30 seconds to a minute before you hear the gas making a hissing sound. The ignitor did not glow,therefore the flame sensor (a small metal probe about 1/8" in diameter, with a white porcelain base) does not sense the flame, so after 8 to 10 seconds the gas hissing sounds stops with no ignition of gas to heat your home. Your furnace shuts down and goes into a lock out condition until you turn your power switch back off and on again. Then the sequence starts all over again with no ignition of the gas. Solution:You probably need to purchase and install a new ignitor. I would suggest that you inspect your ignitor closely for cracks. Please Make sure you do not touch the ignitor with your bare hands. If you do not visually see a crack, then you could possibly have a furnace control board problem or a bad limit switch or rollout switch problem.

Sounds like a faulty board. shut the power to the furnace off for a minute then turn it back on. Make a call for heat at the thermostat. The inducer should start and close contacts on a pressure switch . Once pressure switch closes the hot surface ignitor should glow red. Then the gas valve will open when the gas valve opens you should get fire till the stat is satisfied. If your concerned it is the jump out r to w on the board this will eliminate the stat. If you to reset the rollout switchs 3 timesyou're getting flame rollout and you either have a cracked heat exchanger or blockage in the exhaust piping or a bad inducer motor. Keep me posted with what you find!

Problem: Your furnace will not ignite the gas to produce heat for your home. When a furnace has a bad ignitor what I see most of the time is the following sequence of operation:

1. Thermostat calls for heat. 2. Draft inducer motor starts. 3. Pressure switch attached by a small plastic or rubber tube senses the negative pressure produced by the draft inducer and closes. 4. Draft inducer runs for 30 seconds to a minute before you hear a gas hissing sound. The ignitor did not glow, the flame sensor (a small metal probe about 1/8" in diameter, with a white porcelain base) does not sense the flame, so after 8 to 10 seconds the hissing sounds stops with no ignition of gas to heat your home. Your furnace shuts down and goes into a lock out condition until you turn your power switch back off and on again. Then the sequence starts all over again with no ignition of the gas. Solution: You probably need to purchase and install a new ignitor. I would suggest that you inspect your ignitor closely for cracks. Make sure you do not touch the ignitor with your bare hands. If you do not visually see a crack, then you could have a furnace control board problem or a limit, rollout switch problem. The furnace's control board might not be supplying the voltage to the ignitor. If your furnace lights and the gas stays on for 8 to 10 seconds, then shuts right back off, then you need to clean your flame sensor with light sand paper or steel wool. You might need a new flame sensor, but most of the time they can be cleaned an will work well after cleaning.

Problem: Your furnace will not ignite the gas to produce heat for your home. When a furnace has a bad ignitor what I see most of the time is the following sequence of operation:

1. Thermostat calls for heat. 2. Draft inducer motor starts. 3. Pressure switch attached by a small plastic or rubber tube senses the negative pressure produced by the draft inducer and closes. 4. Draft inducer runs for 30 seconds to a minute before you hear a gas hissing sound. The ignitor did not glow, the flame sensor (a small metal probe about 1/8" in diameter, with a white porcelain base) does not sense the flame, so after 8 to 10 seconds the hissing sounds stops with no ignition of gas to heat your home. Your furnace shuts down and goes into a lock out condition until you turn your power switch back off and on again. Then the sequence starts all over again with no ignition of the gas. Solution: You probably need to purchase and install a new ignitor. I would suggest that you inspect your ignitor closely for cracks. Make sure you do not touch the ignitor with your bare hands. If you do not visually see a crack, then you could have a furnace control board problem or a limit, rollout switch problem. The furnace's control board might not be supplying the voltage to the ignitor. If your furnace lights and the gas stays on for 8 to 10 seconds, then shuts right back off, then you need to clean your flame sensor with light sand paper or steel wool. You might need a new flame sensor, but most of the time they can be cleaned an will work well after cleaning.

The pressure switch requires a negative pressure (vacuum) to close the contacts. It is measuring the pressure in the inducer and indirectly ensure there is good combustion airflow throught the heat exchanger. Check for a small vacuum, in the neighborhood of 1" water column. Usually the vacuum required to close the switch is stamped on the vacuum switch. Check the vent pipe for obstructions and correct size and installation.
If the pressure aka vacuum switch does not close the furnace will not continue with ignition, for safety reasons.

That control board is several hundred dollars. If I may make a suggestion, take a jumper and when the inducer fan starts, jump out the pressure switch. If it starts, it's not the board but a bad switch, hose or blocked exhaust vent.

On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the igniter. The igniter will glow and you will be able to see it if viewed thru the small inspection port. Once the igniter gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.

What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the igniter does not energize (bad control, bad igniter), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not light (dirty pilot), the burner does not light (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).
Your furnace has a diagnostic chart on the reverse of the lower panel incorporated in the wiring diagram. One blink tells you that it is a failure but wont tell you where to start looking.

Furnace attempted to start but failed after so manay tries. This may help you.

Sequence of operation, Gas Furnace.

On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the ignitor. The ignitor will glow and you will be able to see it if viewed thru the small inspection port. Once the ignitor gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.

What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the ignitor does not energize (bad control, bad ignitor), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not lite (dirty pilot), the burner does not lite (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).

Most newer furnaces will have a diagnostic center or control built into the control module. You may be able to view it as it is running thru a small viewing port. Some models will require the removal of an access panel prior to finding it. On the reverse of the access panel, there will be a diagnostic chart that will aide you in understanding any error code recorded (usually a blinking light).

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